Chromium-nickel plating

ABSTRACT

THIS INVENTION COMPRISES A COMPOSITE OR LAMINATED METALLIC COATING, AND A PROCESS FOR MAKING SUCH COATING, COMPRISING A FIRST LAYER OF NICKEL AND AN OVERLYING LAYER OF CHROMIUM, THE LAMINATE BEING CRACKED IN A CRAZE PATTERN IN THE RANGE OF 300 TO 3000 CRACKS PER LINEAL INCH PREPARED BY ELECTRODEPOSITING ON A METAL SUBSTRATE A STRESSED LAYER OF NICKEL AND THEREAFTER ELECTRODEPOSITING ON THIS STRESSED LAYER OF NICKEL A STRESSED LAYER OF CHROMIUM ADHERENT TO THE STRESSED LAYER OF NICKEL AND HEATING THE RESULTANT LAMINATE. THE STRESSING IN THE RESPECTIVE LAYERS MAY BE EFFECTED BY MEANS OF AN ADDICTIVE IN THE ELECTROPLATING SOLUTION FROM WHICH IT IS PRODUCED. THE RESULTANT CRAZING GIVES AN IMPROVED PROTECTION AGAINST CORROSION.

United States Patent 3,563,864 CHROMIUM-NICKEL PLATING Arthur H. DuRose, Euclid, Karl S. Willson, Cleveland, and Gustavo C. Tejada, Euclid,Ohio, assignors, by mesne assignments, to Kewanee Oil Company, BrynMawr, Pa., a corporation of Delaware No Drawing. Filed Apr. 26, 1965,Ser. No. 451,028 Int. Cl. 'C23b 5/50, 5/52 US. Cl. 204-37 ClaimsABSTRACT OF THE DISCLOSURE This invention comprises a composite orlaminated metallic coating, and a process for making such coating,comprising a first layer of nickel and an overlying layer of chromium,the laminate being cracked in a craze pattern in the range of 300 to3000 cracks per lineal inch prepared by electrodepositing on a metalsubstrate a stressed layer of nickel and thereafter electrodepositing onthis stressed layer of nickel a stressed layer of chromium adherent tothe stressed layer of nickel and heating the resultant laminate. Thestressing in the respective layers may be effected by means of anadditive in the electroplating solution from which it is produced. Theresultant crazing gives an improved protection against corrosion.

This invention relates to composite, metallic coatings or laminatedcoatings comprising a first layer of nickel and an overlying layer ofchromium. More specifically, the present invention relates to thediscovery that when both layers of a two-layer nickel-chromium laminateare suitably stressed, the composite can be caused to becomemicrocracked in a fine pattern and the resulting microcracked laminatehas superior properties, especially in regard to protection againstcorrosion.

In accordance with the present preferred embodiment of the invention anickel deposit having a high tensile stress is used, which, whencombined with a suitable chromium overlying layer, produces coatings ofimproved corrosion resistance. Nickel deposits according to the invention are stressed and, when combined with the chro mium deposit,which is also stressed, the stresses reinforce each other and thecomposite exhibits a microscopic crazing or cracking in a craze patternwhich is made up of fine lines, from about 300 to 3000 cracks per linealinch. Although still finer crack patterns are acceptable, it ispreferred to produce 700 to 2000 cracks per inch. The deposits havingpatterns in the preferred range tend to give the best protection againstcorrosion. The nickel layer may be applied to a thickness from 0.03 milto 0.5 mil, preferably 0.05 to 0.25 mil, and the thickness of thechromium layer being preferably from 10 millionths of an inch to 50millionths of an inch.

Prior to the present invention it has been known to plate over brightnickel a layer of chromium from a solution containing selenium ion(Safranek and Miller, Plating 51 543) but, so far as known toapplicants, the bright nickel referred to was not prestressed within thehereinbelow suggested values and does not give equivalent results tothose obtained where both deposits are prestressed and cooperate toproduce cracks within said lirnits'of 300 to 3000 cracks per linealinch.

When a selenium compound, e.g. sodium selenate, at a concentration ofthe order of 0.015 gram per liter is added to a chromium plating bath,the resulting chromium deposit, when plated over nickel to a thicknessof, for example, 30 millionths of an inch will produce microcrackingwhen the plated object is suitably heated, as, for example, by immersionin hot water. Said seleniumcontaining bath, however, does not have goodthrowing power and the deposit from such a bath has little or nochromium deposited in the low current density areas of the object beingplated. In order to provide better coverage by the chromium and stillretain the improved corrosion resistance of the microcracked chromium,it is customary to deposit in the order of 10 millionths of an inchthickness of chromium from a standard chromium bath (containing noselenium) and follow this with a deposit from the selenium-containingchromium bath of the order of 15 millionths or more in thickness. Inaddition to the reduced throwing power of the chromium bath containingthe customary amount of selenium compound, the chromium deposits fromsuch selenium-containing bath tends to have a bluish color which isundesirable. According to the present invention, the amount of seleniumcan be reduced or selenium can be omitted, as will be shown later, withincreased throwing power as a result; also, the undesirable bluish coloris reduced. The nickel deposit must be prestressed in order to get thesegood results.

Microcracking also has been produced in two-layer chromium systems byvariations in the character of the separate chromium deposits due todifferences in operating conditions or by variations in compositions ofthe plating baths (US. Pat. 3,157,585).

The present invention dilfers from the earlier methods of producingmicrocracking in that the two-layer composite responsible for themircrocracking comprises a thin layer of nickel of special character,prestressed, and

a layer of chromium.

According to one method of producing a desirable microcracked coating ofthe present invention, a smaller than usual concentration of theselenium compound in the chromium bath can be used to produce thecorrosion resistant coating. This is accomplished by plating first astressed nickel deposit and then a layer of chromium from the chromiumbath containing less than the usual concentrations of selenate. Thefirst coating (nickel) is stressed but not cracked and the chromiumlayer from the selenium-containing bath is then laid down, therebyproducing enough stress to crack the chromium when, for example, thedeposit is heated as by dipping the coated substrate in hot water, e.g.boiling water or water at F. Certain selenium-free chromium platingsolutions may be employed. The usual chromium plating solution producesa moderately stressed deposit and adding the selenium reduces throwingpower. Adding less selenium gives better results as indicated above. Thehighly stressed nickel deposit makes possible omission of some or allthe selenium without substantial loss in throwing power, still gettingthe improved throwing power as if selenium had not been used. Thesmaller than customary amount of selenium in the chromium bath does notresult in the very large loss of throwing power caused by the normalamount of selenium. Further, the objectionable blue color of thechromium deposit from the usual selenium-containing bath is avoided orreduced.

According to one method of the present invention, a single additive(other than an antipitter which may be used if desired) to the Wattstype nickel bath may be used to provide a stressed nickel of improvedlustre. Small concentrations of certain additives yield a high degree oftensile stress in nickel deposits when sulfooxygen control agents areabsent. Using a smaller than usual concentration of the seleniumcompound in the bath used for deposition of chromium over the stressednickel, the lesser amount of selenium results in a laminate which willcrack in a desirable fine pattern and good corrosion resistance willresult.

In the laminates according to the present invention, it is importantthat the stress in both the nickel deposit and the chromium deposit besuch that microcracking of the laminate occurs. Microcracking may occurspontaneously toward the end of or after electrodeposition of thechromium, or by immersion in hot water, or during outside exposure, orduring accelerated corrosion testing.

Although the reasons for the appearance of stress in chromium depositshave been the subject of much experimentation and speculation, there isno general agreement as to the cause. It has been suggested that acodeposited chromium hydride or absorbed hydrogen may be responsible forthe stress.

In our tests, we have found that when a stressed laminate of our presentinvention is inserted into boiling water, there is an immediateevolution of gas and the deposit is thereafter microcracked. A usualchromium deposit does not evolve gas under the same circumstances.

It is important that the microcracking show a pattern of the order of300 to 3000 or more cracks per lineal inch, preferably from 700 to 2000cracks per lineal inch. The crack pattern is controlled by the degree ofprestressing. Numerous methods can be used to prestress the nickeldeposits. Examples are hereinbelow stated.

A microcracked deposit as herein considered, within the specified limitsof 300 to 3000 cracks per lineal inch, contains a random pattern ofinterlocking cracks which cannot be seen directly under the microscopeusing a magnification of the order of 150 times. In order to determinethat microcracking has occurred, use is made of the Dubpernell test inwhich the composite electroplate including a top layer of chromium ismade cathodic in an acid copper sulfate solution at low current density.Copper is deposited only at the microcracks and not on the uncrackedarea where it is believed the chromium is covered by an oxide film.

In the case of thin deposits of chromium over nickel Where microcracksdevelop, it is known that cracking extends to or into the nickel layer.With thicker deposits of chromium, the microcracking may not necessarilyextend to the nickel deposit in all cases. Under these circumstances,copper is also deposited at the microcracks in the chromium using theDubpernell test. In this case, it is believed that the oxide film doesnot cover the bottom of the crack.

Tests have showed that where microcracking occurs within the limitsherein specified, improved protection against corrosion is secured.

In this specification and in the appended claims nickel includes cobaltand nickel-cobalt codeposits, but nickel is preferred.

All plating solutions herein described are aqueous.

It is contemplated that the hereindescribed laminates of stressed nickeland chromium may be applied over a variety of substrates, including ausual bright nickel substrate or a semibright nickel substrate, saidbright or semibright nickel substrates being electrodeposited overmetallic surfaces generally, for example, iron or steel. The stressednickel may be applied upon metals or conductive surfaces quitegenerally; for example, cobalt, nickel, copper, brass, or other metals,and alloys of two or more thereof.

A two-layer deposit according to the invention may be laid down bydepositing a layer of stressed nickel on any of the substrates indicatedabove. On the stressed nickel layer there may be deposited a layer ofstressed chromium. The nickel layer may be stressed by means of anadditive to the solution. The chromium layer, likewise, may be stressedby an additive to the solution in which it is produced. The stressednickel producing solutions may be produced, for example, by using as anadditive an amine borane compound, or a pyridinium compound, or aquinolinium, or isoquinolinium compound. These additives in the nickelbath, and selenium compounds, for example, in the chromium bathcooperate to make a deposit plate more uniformly over the work be morefree from objectionable bluish color. The selenium may be partly orcompletely omitted from certain chromium solutions while retaining manyof the benefits of the invention. It is preferred, however, toincorporate a limited concentration of selenium into the chromiumplating solution.

The process for producing the desirable laminates is critical in threerespects. First, the chromium solution either with or without seleniummust yield a stressed deposit, sufliciently stressed to cooperate withthe nickel deposit to yield a microcracked laminate. Second, thestressed composite must yield a double stressed laminate capable ofcracking in a fine pattern of from about 300 to 3000, or more, cracksper lineal inch. Third, the nickel deposit from the nickel platingsolution must yield deposits which will be stressed such that thedesirable crack pattern of from about 300 to 3000 or more cracks perlineal inch is obtained. Any additive to the nickel solution can be usedto produce a nickel deposit which can be used in connection with achromium deposit taken from a chrome solution comprising chromic acidand sulfate ion, provided the deposit is sufficiently stressed. Thenickel deposit should be stressed prior to cracking to the extent of atleast about 30,000 pounds per square inch (rigid strip method). Thestressing of the deposits can be varied by adjusting the amount ofadditive in the solutions or as hereafter described.

In addition to the prior art above cited, attention may be called to US.Pat. No. 2,658,867 which describes a cracked deposit having of the orderof 50 to 200 cracks per lineal inch when overplated with .01 mil ofchromium from a standard chromium bath. U.S. Pat. No. 2,644,789discloses the use of pyridinium compounds as brighteners in connectionwith sulfo-oxygen carriers, for the deposition of bright nickel. Whensuch a bright nickel is overplated with a standard chromium deposit, amicrocracked deposit does not develop even on heating to 200 F. Nonickel deposits suitable for the present invention have been describedin such disclosures so far as applicants are aware.

Sulfo-oxygen carriers (control agents), such as benzene sulfonate andsaccharin, are undesirable in the solution used to produce stressednickel of the present invention since they lower the tensile stress. Ifused in the bath, the concentration of the carrier should be lower thancustomary in a bright nickel bath and should not exceed 0.1 gram perliter.

The Watts type of nickel plating solution is preferred whenstress-inducing agents are used. It may, for the purposes of thisinvention, consist of nickel sulfate in high concentration, nickelchloride in lesser concentration, and boric acid also in lesserconcentration. Sodium lauryl alcohol sulfate may also be included but isnot essential since the bath will function more or less well without it.In addition to the Watts bath, other baths ranging from all sulfate toall chloride solutions may be used. Baths containing sulfamates may beused. Alkaline solutions may be used as well as nickel fiuoborate, andmany more as basic nickel plating solutions.

Two such groups of nitrogen compounds which may be suggested aspreferable are the amine boranes and the pyridinium, quinolinium, andisoquinolinium compounds. A number of specific examples of these boranecompounds are listed in Table I.

The invention contemplates preferably the two-layer laminate coatings,both layers together under stress high enough to allow microcracking andthe process of producing the said laminates with suitable stress, andcracking such laminates so stressed. Further, more specific andpreferred features of the invention are:

producing the laminates by the use of a suitable stressinducing agent inthe chromium plating solution, and producing the laminates by the use ofa Watts type bath containing a compound of the class consisting of theamine boranes, such as those listed in Table I, and pyridinium,quinolinium, and isoquinolinium compounds, such as those listed in TableII, and miscellaneous compounds, such as those listed in Table HI.

In the process of manufacturing laminates according to the invention,the thickness of the deposits and the temperatures of electrodepositionare important although considerable and numerous variations can beutilized. For best results the nickel deposit should be plated to athickness of from 0.03 to 0.52, preferably 0.05 to 0.25 mil at atemperature in the range of 60 F. to 160 F. The layer of chromium shouldbe of a thickness from to 50 millionths of an inch applied in thetemperature range of from 90 F. to 150 F. When the deposits have beenapplied, the laminate preferably should be heated to a temperature inthe range from 180 F. to 450 F. in a period of time from 5 to 120seconds. It may be desirable to alternately chill and heat thecomposite.

The following specific compounds as set forth below may be used in theproduction of the laminates above described:

TABLE I In general, the boranes listed in Table I, should be present insolution in concentrations from 0.5 to 2.0 grams per liter.

TABLE II B cranes Preferred concentration grams per liter 1.Trimethylamine borane (CH )3N:BH;

2. Dimethylamine borane (CH )2HN:BH

3. Tertiary butylamine borane (CH CNH2:BH

. Morpholine borane O HZBHQ Pyridine borane C5H5N:BH Picoline borane O HO NH:BH

7. Dimethyl propylamine borane Aniline borane C H NH2:BH Dimethyl aminedimethyl boraue (CH3)2NH:BH(CH3)2 10. Morpholine diethyl borane O 12.Dimethyl dodecyl amine borane 14. Piperazine diborane HEB :NH

15. Benzimidazole diborane The concentrations of the compounds listed inTable II hereof should be maintained in solution in the plating bath tothe extent of from 0.01 to 1.0 gram per liter, the amount used forpreferred results depending on the type of compound employed.

In addition to the above classes of compounds, various miscellaneousclasses and type of stress producing agents may be used as listed inTable III with the preferred amounts shown.

TABLE III (These are representative, not restrictive) Grams per literGelatin .2-.5

Thiourea .01-.15

Acetonitrile .1-1.0 Ethylenecyanohydrin .1l.0 Succinonitrile .1-1.0

Lactonitrile .1-1.0

Cyanoethoxypropyne .005-.05 Thianaphthenedioxide .05l.53-thianaphthenone-l-dioxide 305-15 N-allyl-4-nitro-5(-3'pyridinium)pyrazole iodide .005.015 H PO .33.0 S602 .2.5 TeO .2-.53-sulfolene 5-2.0 3-thiocyauopropane-l-potassium sulfonate .52.03-nitropropane sodium sulfonate .52.0 3-(dimethylsulfoxonium)propanesodium sulfonate .5-2.0 N-allyl quinaldinium bromide .006-.1Polyalkylene amines (M.W. 100-1000) .01.2 ,Polyalkylene amine adductswith acrylonitrile,

acetylenic compounds .01-.2 5-nitroindazole .02-.05

NaNO;; 1 .5-1.0 2-butyne-1,4 diol 2 and ethoxylated butynediol 2 .9-1.55-amino-2-mercaptobenzimidazol .01.15 Polyglycols (M.W. 5 10,000).02-1.0 Diethyleneglycolmonopropargyl ether .05-.2p,p-Methylene-bis-triphenylphosphorium bro mide .02.2

1-amino-2 propyne .6l.5 2-styryl quinoline .006-.06Ethyl-bis-(B-cyanoethyl)-sulfonium ethyl sulfate .005.

B,B'-thiodipropionitrile .003-.03 Diallylpropargylamine 2 .05.lTriethylpropargylammoniurn chloride .l-.5 3-(B-oxypropionamide)propyne-1 .l-5.

Nitrates in low concentrations (.05.3) may actually docrense tensilestress. Higher concentrations increase Ithe stress.

2 Deposits obtained by the use of acetylenics are frequently mlsplatedor striated. These defects can be eliminated by the addition of certainother agents, but in so doing the tensile stress is frequently reduced.Therefore, when they are used to produce the highly stressed nickelneeded in this invention, it is necessary to overcome these defects bythe use of a high current density, i.e. minimum of 40 a.s.f.

Basic nickel plating solutions to which additions according to thepresent invention may be added are as follows:

TABLE IV All sulfate NiSo -7H O 100 to 400, preferably 200 to 300 gramsBoric acid 0 to 60, preferably 10 to 40 grams.

H O to make 1000 cc.

8 High chloride NiSO -6H O 75 to 225, preferably to 200 grams. NiCl -6HO 50 to 150, preferably 75 to 150 grams. Boric acid 0 to 60, prefrably10 to 40 grams.

H O to make 1000 cc.

Sulfate-chloride (Watts type) NiSo -7H O 100 to 400, preferably 200 to300 grams.

NiCl -6H O 10 to 60, preferably 25 to 40 grams.

Boric acid 0 to 50, preferably 15 to 40 grams.

H O to make 1000 cc.

The basic chromium solution may be a water solution of chromic acid withsulfate ion to the extent of about 0.6 to 1.5 percent of the chromicacid. To this may be added, to produce microcracking in combination witha stressed nickel, a selenium compound, such as Na SeO or an organiccompound, such as AS203.

Other baths, for example those containing strontium and fluosilicateions may be used.

The following chromium solution (See Table V) produces a good microcrackwith prestressed nickel but not with unstressed nickel. The stress inthe nickel deposit was obtained by use of a bis-pyridinium compoundadditive in the Watts bath. The bis-pyridinium compound may be used at aconcentration of preferably from 0.1 to 1.0 gram per liter.

CrO 250-375 grams per liter H 80 2.5 grams per liter Na SeO 0.005 gramsper liter Temperature F.

Cathode current density a.s.f. for 10 minutes This solution may also beused to produce microcracking over stressed nickel stressed by use of anamine borane.

Sodium selenate, for example, may be used in the above solution. It maybe added in concentration from no selenium to about 0.10 gram per liter:preferbaly, about 0.0025 to 0.0075 gram per liter should be used. (Note:sodium selenate of the order of 0.015 gram per liter should be used toproduce microcracking over ordinary bright nickel.)

Groups of additives have been set forth by way of examples as to how toproduce the stressed nickel deposits of the invention. One of thesegroups is the amine boranes; another group is the bis-pyridiniums,bis-quinoliniums, and bis-isoquinoliniums. There is also a miscellaneousgroup (Table III.) The plating conditions have been stated suificientlyto enable the chemist skilled in the art to produce the stresseddeposits. The nickel is first deposited having requisite stress, afterwhich there is applied a coating of chromium having the requisitestress. The chromium solution may contain selenium as above stated.Having applied both layers, with proper stress, the composite willmicrocrack during the chromium plating step, shortly thereafter on mildheating, or on corrosion testing, such as the Corrodkote test, or onoutdoor exposure (which may take an undesirably long time.) Heating withhot water apparently is the most practical cracking step.

It is generally agreed that cracking of a chromium deposit is due notonly to the stress, ductility, and tensile strength of the chromiumdeposit but is also affected by the stress of the immediately underlyingsubstrate. There is also evidence that to a large extent, the stressesare additive, so that the stress in the chromium deposit may not be highenough to fracture the chromium but the additive effect of the stressesin chromium and nickel will cause cracking of the chromium. It is wellknown, therefore, that when a standard chromium deposit is applied .overa higher than normally stressed nickel deposit (20,000'-30,000 p.s.i.)cracking or crazing occurs but this is macrocracking and is visible andunsightly. We have discovered, however, that when both the nickel andchromium of this laminate are highly stressed the macrocracking isavoided and the desired microcracking is obtained.

The values obtained for stress of electrodeposits are affected bynonreproducibility of calculated stress values when measured bydifferent methods, the nature of the substrate, the thickness of thedeposit, and the cracking of the deposit during the plating processwhich relieves the apparent stress.

For a given Watts solution, the rigid strip method of measuring stresswill give values of 12,000 to 17,000 p.s.i.; the helical contractometermethod for the same solution gives values of 20,000 to 27,000 p.s.i. Foran all chloride solution, the following values may be obtained:

P.s.i. Rigid strip 33,000-41,000 Contractometer 53,000-62,600

If there is no cracking, the stress of a deposit will depend on itsthickness primarily because of the effect the substrate structure has onthe deposit structure. This eflect may disappear after 500 angstroms orstill be present at thicknesses of .1 to .2 mil. In most cases (see C.Williams, Met. Finishing J. 8 (85) (1962)) for nickel or chromium ontheir normal substrates (Fe, Cu, Ni), the tensile stress will decreasewith increase in thickness. It is possible, however, for the reverseeffect to occur (see 11. Watkins, J. Electrochem Soc., November 1961.)

It is well known that measurement of stress in chromium deposits isfraught with difficulties due to the cracking of the chromium depositduring deposition. Brenner (Proc. Am. Electroplaters Soc. p. 32, 1947)reports 80,000 p.s.i. for very thin uncracked deposits, but 17,000p.s.i. for thicker deposits which have evidently relieved themselves bycracking during the plating process. This same effect can occur withnickel deposits which are highly stressed. For example, an 0.25 mildeposit of nickel from the nickel solution of Example II has a stress ofabout 40,000 p.s.i., but a 1 mil deposit shows a stress of only 15,100p.s.i. and this is primarily because fine cracking has occurred in thelatter case.

For the above reasons, it is difiicult to specify stress values whichare desirable for the stressed nickel and stressed chromium of thisinvention. The stressed nickel fiash is best described operationally asone which will effect microcracking when a higher than normal stressedchromium deposit is applied over it and will not give microcracking whenstandard chromium is applied over it. Likewise, the stressed chromiumdeposit is described operationally as one which will give microcrackingwhen applied over a higher than normal stressed nickel depcsit but willnot give microcracking when applied over a normal nickel deposit such asthat from a Watts bath at pH 3.5 or such as that from a bright nickelsolution containing a sulfo-oxygen control agent.

The stressed nickel deposit should not be too thick; if greater than0.15 to 0.2 mil, it may tend to crack before chromium plating and giveundesirable macrocracking visible to the naked eye. Provided the nickelflash is under enough stress, finer microcracking is obtained, afterchromium plating, for thin nickel deposits. Stressed nickel deposits inthe order of 0.1 mil or less are preferred. The stress of the nickeldeposit when measured by the rigid strip method and at 0.2 mil should beat least 30,000 p.s.i.

Another practical reason for the use of thindeposits is that in somecases, especially where the stress inducing agents are not alsobrightening agents, or where special 10 addition agents are not evenused, the deposit will tend to become dull with increasing thickness. Inthese cases, the stressed nickel deposit should not be thicker than 0.05mil.

Addition agents are not always needed in order to obtain high tensilestresses in the nickel deposit. In general it has been found that thestress in the nickel deposit, as evidenced by the ease of obtainingmicrocracking when the stressed chromium is applied, increases withincrease in chloride content of the solution, with decrease intemperature, and with increase in current density. The pH should beeither high (greater than 5.0) or low (less I than 2.0). Also, the acidsolutions should not be too highly buffered. Alkaline nickel solutions,such as described in U.S. 2,773,818, US. 2,069,566, British 512,484, andBritish 880,786 may be used, although simple solutions containing onlynickel citrate or tartrate are as effective as some of those solutionsproposed for heavier nickel deposits. The addition of acetylenic typebrighteners, such as butynediol to alkaline solutions, further increasesthe tensile stress in the nickel flash and excellent corrosion resultshave been obtained.

Representative nickel solutions which may be used without stressinducing agents are given in Table V:

TABLE V NiSO -6H O grams per liter. H BO 7 grams per liter. pH 5.5.Temperature 40 C. C.D. 100 a.s.f.

NiSO -6H O- 50 grams per liter. pH 1.7. Temperature 30 C. C.D. 50 a.s.f.

N1Cl '6H O 300 grams per liter. H BO 7 grams per liter. pH 1.7.Temperature 30 C. C.D. 200 a.s.f.

NiCl 6H O 200 grams per liter. H BO 22 grams per liter. pH 5.5.Temperature 30 C. C.D. 200 a.s.f.

NiSO- '6H O 200 grams per liter. NiCl '6H O 60 grams per liter. H BO 30grams per liter pH 5.8. Temperature 50 C. C.D 20 a.s.f.

NiSO '6H O 200 grams per liter. NiCl '6H O 60 grams per liter. H BO- 30grams per liter. (NH SO 35 grams per liter. pH 1.5. Temperature 30 C.C.D 50 a.s.f.

NiSQ -6-H O 100 grams per liter. Na citrate 200 grams per liter. pH 6.5.Temperature 50C.

C.D 40 a.s.f.

TABLE VCont-inued NiSO -6H O 100 grams per liter. Na citrate 66 gramsper liter. NH Cl grams per liter. EDTA 50 grams per liter.Triethanolamine 50 ml. per liter. Ni(NO 20 grams per liter. pH 9.0.Temperature 120 F. OD. 50 a.s.f.

While the microcracked composite coating may be applied directly to abasis metal, such as steel, copper, etc., we believe it will find itsgreatest use when applied over a substrate of bright or semibrightnickel coatings, or combinations of semibright and bright nickelelectrodeposits. Thus, the composite coating of the invention may bedeposited over a bright nickel electroplate, such as deposited accordingto U.S. Pat. 2,712,522, or preferably over a duplex nickel depositcomprising a semibright electroplate according to, for example, U.S.Pat. 2,635,076, followed by a bright electrodeposit according to, forexample, U.S. Pat. 2,978,391. The composite according to the presentinvention may also be used with a triplate nickel coating according toU.S. Pat. 3,090,733.

The following specific examples will help to illustrate the invention:

EXAMPLE I Over a 1 mil thick electrodeposit of bright nickel on steel,an additional electrodeposit of stressed nickel was laid down (to athickness of 0.1 mil.) This stressed nickel was deposited from anaqueous solution made up as follows:

NiSO -6H O 240 grams per liter. NiCl '6I-I O 40 grams per liter. H BO 40grams per liter. pH 3.5.

Cathode current density 40 a.s.f. Temperature 140 F. Trimethylamineborane 1.0 ml. per liter.

Onto the above cited stressed nickel deposit, we plated chromium to athickness of 20 millionths of an inch, from a bath containing:

CrO 250 grams per liter. H 80 2.5 grams per liter. Na SeOg, .005 gramsper liter. Temperature 100 F.

Current density 140 a.s.f.

EXAMPLE II Over a bright nickel deposit on steel, as cited in Example I,we electroplated a 0.1 mil deposit of stressed nickel from a bath ascited in Example I except that the amine borane was replaced by 0.4 gramper liter of N,N-trimethylene-bis-pyridinium bromide. Over the stressednickel was then deposited chromium as cited in Example I. Results weresimilar to those reported for Example I.

EXAMPLE III Using the bright nickel on steel followed by the stressednickel electrodeposit of Example II, we deposited 30 12 millionths of aninch thickness of chromium from the following bath:

CrO 375 grams per liter. NaOH 50 grams per liter. Cr O 7 grams perliter. H 0.7 grams per liter. Temperature F.

Current density a.s.f.

A good microcracked pattern was secured on dipping for one minute inwater at 200 F.

No microcracking occurred when chromium from the above bath wasdeposited over bright nickel directly, omitting the stressed nickeldeposited from the bath containing the pyridinium bromide compound.

EXAMPLE IV Using the bright nickel on steel followed by the stressednickel deposit of Example II, we deposited 30 millionths of an inch ofchromium from the following bath:

CrO 200 grams per liter.

K Cr O 36.8 grams per liter. SrCrO 4.5 grams per liter.

K SiFe 10.5 grams per liter. SrSO, 6.0 grams per liter.

Temperature 120 F.

Current density 250 a.s.f.

The resulting composite gave a good microcrack pattern after dipping for2 minutes in water at 200 F.

EXAMPLE V EXAMPLE VI Using the composite nickel electrodeposit on steel,including the stressed nickel layer of Example II, chromium wasdeposited to a thickness of 30 millionths of an inch in the followingbath:

CrO grams per liter. H 80 2.5 grams per liter. As O 3.95 grams perliter. Temperature 118 F.

Current density a.s.f.

After treating the deposit in water at F. for two minutes, microcrackingwas secured. When the stressed nickel layer was omitted, microcrackingdid not occur.

EXAMPLE VII Steel plated with 1 mil bright nickel was further platedwith 0.1 mil of stressed nickel at 40 a.s.f. and 140 F. from a Wattsbath (pH containing 0.015 gram per liter of2-oxydiethylene-bis-isoquinolinium chloride. When a 30 millionth of aninch deposit of chromium was applied from the bath cited in Example I,microcracking was produced by the hot water treatment and good corrosionresistance was secured.

EXAMPLE VIII Results similar to those of Example II were secured whenthe pyridinium bromide compound of Example II was replaced by 0.2, 0.4,or 0.6 gram per liter of N,N oxydimethylene-bis-pyridinium chloride.

EXAMPLE IX Excellent corrosion results were secured when 1 gram perliter of morpholine borane replaced the trimethyl amine borane used indepositing the stressed nickel layer 13 in Example I and millionths inchthickness of chromium was deposited from the bath cited in Example I.

EXAMPLE X Excellent corrosion results were secured when 1 gram per literof morpholine borane replaced the trimethyl amine borane used indepositing the stressed nickel layer in Example I and 10 millionths inchthickness of chro mium was deposited from the bath cited in Example I,when the stressed nickel layer was deposited at room temperature anda.s.f.

EXAMPLE XI Composites showing excellent resistance to corrosion weresecured using the following electrodeposits successively over steel.

(a) Semibright nickel 0.8 mil (b) Bright nickel 0.4 mil (c) Stressednickel 0.1 mil from a Watts bath containing 2 grams per liter ofmorpholine borane at room temperature and 15 a.s.f.

(d) 10 millionths of an inch of chromium from the bath cited in ExampleI EXAMPLE XII Same as Example XI except that in (c) the stressed nickelwas deposited from a Watts bath containing 0.2 gram per literethylene-bis-pyridinium bromide at 140 F. and 40 a.s.f., and thechromium deposit thickness was millionths of an inch.

EXAMPLE XIII Onto a bright nickel deposit on steel, an 0.1 mil depositof stressed nickel was electroplated from a Watts bath containing 0.5gram per liter of N,N'-methyl-N'-piperazino-l hydroxy butene, at 140 F.and 40 a.s.f. After further electroplating 20 millionths of an inch ofchromium from the bath of Example I, and heating the deposit at 190 F.when microcracking occurred.

EXAMPLE XIV Same as Example XIII except that the Watts bath contained0.4 gram per liter of 1,6-dimethyl piperazine instead of the piperazinocompound.

EXAMPLE XV Onto a bright nickel substrate, there was deposited anadditional deposit of stressed nickel according to Example I except thatthe amine borane was replaced by 1 gram per liter of H PO (phosphorusacid). Onto this stressed nickel was deposited 0.03 mil of stressedchromium from a bath made up and used as follows:

, CrO 80 grams per liter. H 80 0.5 gram per liter. Temperature 130 F.

Cathode current density 100 a.s.f.

After immersing for 1 minute in hot water (100 F.), the deposit wasmicrocracked.

The invention claimed is:

1. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate, said duplex coating consisting of chromium overnickel which comprises electrodepositing a smooth continuous nickellayer having high internal stress on a substrate and thereafterelectrodepositing a chromium layer on said smooth continuous nickellayer, said chromium layer being sufiiciently stressed so that itinteracts with said smooth continuous nickel layer to cause both saidnickel and chromium layers to crack into a micro-cracked pattern duringor subsequent to the electrodeposition of said chromium layer.

2. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 1 wherein said micro-crackedduplex coating has a crack density in the range of from about 300 to3,000 cracks per lineal inch.

3. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 2 wherein said nickel layer isof the thickness of from 0.03 to 0.5 mil and said chromium layer is of athickness from 10 millionths to 50 millionths of an inch.

4. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 3 wherein said micro-crackingis accelerated by moderately heating said duplex coating such as bycontacting the same with hot water.

5. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 4 wherein said nickel layer iselectroplated from an aqueous nickel plating solution comprising anickel compound supplying nickel ions and an internal stress producingaddition agent selected from the group consisting of amine boranes,pyridinium compounds, quinolinium compounds and isoquinoliniumcompounds.

6. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 5 wherein said chromium layeris electroplated from an aqueous plating bath comprising chromic acid,sulfate ion and selenate ion.

7. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 4 wherein said chromium layeris electroplated from an aqueous plating bath comprising chromic acid,sulfate ion and selenate ion.

8. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 1 wherein said nickel layer iselectroplated from an aqueous nickel plating solution comprising anickel compound supplying nickel ions and an internal stress producingaddition agent selected from the group consisting of amine boranes,pyridinium compounds, quinolinium compounds and isoquinoliniumcompounds.

9. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 8 wherein said chromium layeris electroplated from an aqueous plating bath comprising chromic acid,sulfate ion and selenate ion.

10. A method of depositing a corrosion resistant microcracked duplexcoating on a substrate as stated in claim 1 wherein said chromium layeris electroplated from an aqueous plating bath comprising chromic acid,sulfate ion and selenate ion.

11. A method of depositing a corrosion resistant microcracked duplexcoating in a substrate as stated in claim 1 wherein said chromium layeris electroplated from an aqueous plating bath comprising chromic acid,sulfate ion and silicofluoride ion.

12. A method of depositing a corrosion resistant microcracked coating ona substrate which comprises electrodepositing nickel on said substratefrom an aqueous acidic bath and thereafter electrodepositing chromium onsaid nickel, said nickel being deposited with a high internal stresslevel, said stress level being sufiicient to produce micro-crackstherein during the deposition of the chromium layer which in turnproduces a micro-crack pattern in the chromium layer.

13. The method in accordance with claim 12, in which the said deposit ofnickel is applied to a previous metallic deposit.

14. The method in accordance with claim 13, in which the said previousmetallic deposit is selected from the group of electrolytic coatingsconsisting of semi-bright nickel plating and bright nickel plating.

15. The method according to claim 12 in which the cracking nickel layeris deposited from said aqueous acid nickel bath at a current density ofbetween 15 and 200 amps per square foot.

References Cited UNITED STATES PATENTS Lind et a1. 20449 Nachtman 20437Shenk, Jr. 20449 Schaer 20437 Mikulski 1061 Zirngiebl et a1. 204-49XOdekerken 20441X de Castelet 20441X l6 FOREIGN PATENTS 9/1961 Canada106-1 3/1958 France 20451 5 OTHER REFERENCES Graham, A. Kenneth,Electroplating Engineering Handbook, p. 178, 1955.

GERALD L. KAPLAN, Primary Examiner 10 US. Cl. X.R.

